(function (doc, win) {
var docEl = doc.documentElement,
    resizeEvt = "orientationchange" in window ? "orientationchange" : "resize",
    recalc = function () {
        var clientWidth = docEl.clientWidth;
        if (!clientWidth) return;
        if (clientWidth<640){
            docEl.style.fontSize = 12 * (clientWidth / 320) + "px";
            console.log(12 * (clientWidth / 320) + "px");
            }else{
                //docEl.style.fontSize = "12px";
              docEl.style.fontSize = 12 * ( 640 / 320) + "px";
            }
    };

if (!doc.addEventListener) return;
win.addEventListener(resizeEvt, recalc, false);
doc.addEventListener('DOMContentLoaded', recalc, false);})(document, window);